Patterned Wafer Defect Density Analysis of Step and Flash Imprint Lithography I. McMackin, W. Martin, J. Perez, K. Selinidis, J. Maltabes, F. Xu, D. Resnick, SV Sreenivasan EIPBN 2007
Introduction The purpose of this work is to understand the causes of defects specific to imprint lithography. Outline Describe template pattern, fabrication, and inspection Review historical progress of imprint defectivity Define the major types and sources of imprint defects Review results of defect inspection of wafers imprinted on a prototype imprint lithography tool and on an MII I250 using KT 2132 automated defect inspection tool. Describe dominate sources of imprint defects Results of high resolution imprint inspection using KT es32 Summary
Template Pattern for Defect Inspection Features: Metal-1 and Contact arrays For Inspection by KT-2132 Minimum CD is: 400 nm for M1 350 nm for contacts For e-beam inspection minimum CD is: 70 nm for M1 120 nm for contacts Layout was optimized for ease of inspection on mask and wafer defect inspection tools 100nm SRAM M1 Template Active Area 13 mm 350nm M1 400nm Ct. Inspection area: ~1 cm 2 70, 80, 90nm SRAM M1 120nm DRAM Contact 70 nm SRAM M1
Detailed Template Fabrication and Inspection Pattern Lithography Pattern and Etch Lithography and Etch 1000Å Mesa Lithography and Mesa EtchLitho and Etch Dice Dice Clean Resist Cr Quartz/SiO 2 NTAR7 6.35 mm 15mm Litho PEB DEV Cr Etch Resist Strip Quartz Etch Coat Litho DEV Cr Strip BOE Resist (Mesa) Strip Coat Dice Resist Strip/Clean Cr Strip Clean Inspection Inspection Inspection Inspections performed on plates with multiple template patterns.
Template Defect Inspections (counts) Defect Total 8 7 6 5 4 3 2 Template Defectivity Through Fabrication After Cr and quartz etch After Mesa etch After Cr strip Templates fabricated by commercial mask vendor Inspections were performed with a KT-576 tool by mask vendor 90 nm pixel Reflected light mode Maximum sensitivity 1 0 1 2 3 4 5 6 7 8 Inspection after Cr strip and Mesa Etch was of templates in plate form. Template # 0 defects
KT 576 Inspection Captured Defects Template #4 Post Cr Strip Inspection 7 total defects captured All were contamination defects None persisted in imprints
Progress in S-FIL Defect Reduction at MII Defect Density by Date(KT-2132) Defect Density cm -2 10000 1000 100 10 Non-commercial templates Commercial templates Improved adhesion layer Improved wafer cleanliness and template dicing process 02/2004 06/2004 10/2004 02/2005 06/2005 10/2005 Date 02/2006 06/2006 10/2006 02/2007 Now we show how to proceed to < 5 cm -2
S-FIL Defectivity 1. Template Fab Defects Template 4. Bubbles 2. Material Contaminants 3. Front Side Particles Planarization layer Substrate 5. Back Side Particles Template Planarization layer Substrate Planarization layer Substrate 6. Improper Release Template Planarization layer Substrate 7. Post-Imprint Fall-On Particles
Imprint Defectivity Template #4 Prototype Imprint Tool 1.2 Defect Density by Type Imprinted wafers 68 fields per wafer Inspected area 1 cm 2 per field Pareto at right shows total defect densities for random and repeating defects Defect sizes > 200 nm (KT 2132) Total wafer defect density = 1.7 cm -2 Defect density of: 0.4 0.09 0.03 M1 area = 1.67 cm -2 Contact area = 0.061cm -2 Plug Repeating RLT Depression Ion Contm. random Swelling
Multiple Wafer Run Defectivity: Template 4 Prototype Imprint Tool Internally coated wafers - older generation tools 2% of fields of this run had hot spots, they did not contribute to repeating defectivity Defectivity increases with contamination by imprinting on particles 11 particles caused feature plugging Not all particles cause Defects/cm 2 25 20 15 10 5 0 Wafer Defect Density - Template 4 0 500 1000 1500 2000 Imprint # feature contamination 0 7 15 22 29 Wafer # Total Repeating
Particles that Increase Repeating Defectivity Monomer filled feature w/o direct connection to wafer Particle Ni ion - TOFSIMS Monomer filled feature with good support 5 um Template Li ion - TOFSIMS Wafer Monomer 5 um 5 um Particle locally holds template away from wafer 5 um These large particles cause plugging of feature but did not damage the template
Particles that Do Not Increase Repeating Defectivity Imprint 12 34 5 um Particle that did not cause template feature contamination, no change in repeating defect density Particle that caused limited repeating defect in 4 fields
Imprint Defectivity Imprio 250 Template was not inspected during Fabrication Template has 3 defects defect density = 3.1 cm -2 Imprinted wafers 89 fields Inspected al fields Inspected area per field ~1 cm 2 Pareto at right shows total defect densities for random and repeating defects Defect sizes > 200 nm (KT 2132) Total wafer defect density = 3.4 cm -2 Imprint defectivity = 0.2 cm -2 3.1 Template Ion Contm. Defect Density by Type 0.08 0.07 0.06 Fall on Particle Plug Random 0.04 Prior Particle 0.04
Multiple Wafer Run Defectivity: I250-3 I250 tool with improved ECU and template handling. Internally coated wafers - older generation tools Manually cleaned templates 3 Template defects Inspected 21 fields per wafer Defect Density cm -2 7 6 5 4 3 2 1 Wafer Defect Density Total Defect Density with Template Defects Removed Total Defect Density Repeating Defect Density 0 0 0 100 100 200 200 300 300 400 400 Pilot 1 5 10 500 500 600 600 700 700 800 800 900 900 1000 1000 Imprint # Wafer # 0.2 % fields had particles causing feature contamination
High Resolution Wafer Inspection Defect detection was performed on a KT es32 electron-beam wafer inspection tool and KT-2132 Imprints were made with a prior version of Defect template Minimum CD is 350 nm for Metal-1 and 400 nm for contacts 2 fields on a wafer were inspected, the 1 st and the last, 77 th. M1 and contact areas were inspected Total inspected area on the wafer ~ 2 cm 2 ~ 1 hour inspection time per field Inspection sensitivity: 50% capture rate for a 40 nm defect Additional defects found by es32 inspection 2 new template defects Particles No new imprint related defectivity was found
Comparison of KT-eS32 and KT-2132 inspections Edge-roughness defects: Predominately random and occurring in sizes of 10 to 175 nm. Found only on the bottom edge of horizontal lines False defects Particles defects found by e- Beam did not contribute to repeating defectivity Three template pattern defects were found repeating imprint defects One contaminated contact was detected repeating plug KT-eS32 KT-2132 Type Density cm -2 Density cm -2 Edge roughness 30 0 Particle 11.7 0 Template 3.1 1 Plug 1 1 Repeating Template Defects Found only by es32
es32 Defect Inspection Summary Imprint Defect Density measured by es32 Type Particle Density cm -2 11.7 Template Plug 3.1 1 The total defect density of the two fields measured by the es32 without particles is 4 cm -2. No new imprint specific defects were found by high resolution inspection
Summary Imprint defectivity continuing to decrease, 10 to 2 cm -2 Many fields with 0 imprint specific defects (KT-2132 inspection) High resolution e-beam inspection did not show any increase in imprint related defectivity. Out of 7 classes of defects in the S-FIL process flow only Front- Side particles are responsible for defect levels > approx. 0.1 cm -2 Zero defect templates can be produced (KT-5XX inspection) Further imprint defect reduction focus on Front-Side particles Clean wafer coating and template handling material purity improvement Defect levels of less 1cm-2 are achievable
Acknowledgments NIST-ATP KLA-Tencor Mark McCord Molecular Imprints Brian Fletcher